In a typical can-annular gas turbine engine, a plurality of combustors are arranged in an annular array about the engine. The combustors receive pressurized air from the engine's compressor, add fuel to create a fuel/air mixture, and combust that mixture to produce hot gases. The hot gases exiting the combustors are utilized to turn a turbine, which is coupled to a shaft that drives a generator for generating electricity.
In a typical gas turbine engine, transition ducts are surrounded by a plenum of compressed air from the engine's compressor. This air is directed to the combustors and also cools the transition duct walls. Due to the pressure loss associated with the combustion process, the hot gases within the transition duct that enter the turbine are at a lower pressure than the compressed air surrounding the transition ducts. Unless the joints between the transition duct and turbine inlet are properly sealed, excessive amounts of compressed air can leak into the turbine, thereby bypassing the combustor, and resulting in engine performance loss. A variety of seals have been utilized in this region to minimize leakage of compressed air into the turbine. Some examples include “floating” metal seals, brush seals, cloth seals, and corrugated metal seals, depending on the transition duct aft frame configuration. Older gas turbine combustion systems use “floating” metal seals that are manufactured from a formed plate or sheet metal and are installed such that they can “float” between the aft frame and turbine inlet. Though the “floating” metal seals are quite common, they still have some shortcomings, such as stiffness and tendency to lock in place. Seals that are too stiff cannot adequately comply with relative thermal growth between the transition duct and turbine inlet. If the seals lock in place they cannot adjust to thermal changes and will leave gaps between the transition duct and turbine inlet, allowing compressed air to leak into the turbine.
More recently, corrugated “W” shaped metal seals have been utilized to ensure that a constant contact is maintained between the transition duct and turbine section. The corrugated seal has a spring effect associated with the corrugations and serves to keep the seal in contact with the vane platform of the turbine inlet at all times, thereby reducing leakage as well as having increased flexibility. An example of this type of seal is shown in FIG. 1. Transition duct 10 contains corrugated seal 11 that contacts duct 10 at a first sealing point 12 and turbine vane platform 13 at a second sealing point 14. Corrugated seal 11 is fabricated from relatively thin sheet metal and the multiple corrugations 15 ensure that seal 11 maintains constant contact with transition duct 10 and vane platform 13. While this seal configuration satisfactorily controls cooling air leakage, it tends to wear out prematurely due to its lack of thickness and the constant contact with the harder vane material. As a result of this shortcoming, a wear strip was added to corrugated seal 11 along the contact surface with duct 10 and vane platform 13, in order to extend the sea life. This enhanced seal configuration is shown in FIG. 2 with transition duct 10 containing a corrugated seal 21 that contacts duct 10 via wear strip 22 at a first sealing point 12 and turbine vane platform 13 at a second sealing point 14. As with corrugated seal 11, corrugated seal 21 is also fabricated from relatively thin sheet metal and the multiple corrugations 15 ensure that seal 21 maintains constant contact with transition duct 10 and vane platform 13 along wear strip 22. The addition of wear strip 22, however, caused measurable wear upon vane platform 13 due to the increased hardness of the seal wear strip material compared to the vane platform material and the constant contact between the wear strip and the vane platform due to the spring of the corrugated seal. As a result, turbine vane platforms 13 began exhibiting signs of wear, which must be addressed during a standard repair cycle.
The present invention seeks to overcome the shortfalls described in the prior art by specifically addressing the issues of wear to the transition duct and the turbine vanes by providing an improved sealing system that ensures a sufficient seal that minimizes undesirable cooling air leakage, provides an adequate amount of cooling to the turbine vane platforms, and is fabricated for a lower cost. It will become apparent from the following discussion that the present invention overcomes the shortcomings of the prior art and fulfills the need for an improved transition duct to turbine inlet seal.